From memory you can format any drive as an OSX extended disk and plug it into the USB port on the airport to use it as a time machine drive. If you want to connect straight to a network drive look at this page - it may help.

My wife's has a paper that she is trying access. We had it backed on the external hard, my computer is the only one that is working. Would have to hook up the external hard drive to my Mac? What would happen from there?